U.S. Pat. No. 6,633,462 B2 describes a concept for suppressing harmonics, in which a bridge resistor arrangement is formed of three sub-resistors, a central sub-resistor of greatest resistance, the preferred direction of which lies in the direction of the component to be measured, and two sub-resistors of lower resistance, the preferred direction of which deviates from the preferred direction of the component to be measured by an identical positive or negative angle respectively of 5° to 85°. In this way, any material anisotropy may be reduced and the sinusoidal curve of the measurement signal improved. Each bridge resistor arrangement has a preferred direction corresponding to the preferred direction of the central sub-resistor, diagonally arranged bridge resistors have identical preferred directions.
In further prior art known from EP 2 455 720 A1, as shown in FIG. 2, two sub-resistors RX1 and RX2 of a bridge resistor arrangement RX, i.e. R11 and R12 of the bridge resistor arrangement R1, are connected in series, their pinning directions and thus preferred directions being offset by an angle α. In this way, the 180°/α harmonic is filtered. For instance, the third harmonic may be filtered at an offset angle α=60°. Through a concatenation of a plurality of pinning directions, a plurality of harmonics may be filtered. The overall preferred direction of the measuring bridge is thereby modified towards an angle α/2, as represented by the vector diagram in FIG. 2. As shown in the vector diagram of FIG. 2, in each bridge resistor arrangement R11-R12, R21-R22, R31-R32 and R41-R42 of the overall measuring bridge, which is composed in each case of a series circuit of two sub-resistors RX1-RX2 with different magnetic field-sensitive preferred directions, a preferred direction Rres of the bridge branch results, which corresponds to the direction of the bisector α/2 of the deviation angle α of the two resistors RX1-RX2. Since all the bridge resistors have the same preferred direction in the positive or negative direction in the upper or lower half-bridge branch, the overall sensitivity direction of the overall bridge points in the direction Rres. Diagonal bridge resistors have identical orientations of the preferred directions of the sub-resistors and of the overall resistor.
It is feasible for each of these sub-resistors to be subdivided again and to split further into two elements, whose pinning directions differ by an angle β. As a rule, further splitting takes place symmetrically in a positive and negative angular amount about the preferred angular direction, such that the latter does not change any further. In this way, the 180°/β harmonic may also be filtered. Splitting may be continued and thus theoretically any number of harmonics may be filtered, wherein the number of further sub-resistors in each case increases by a factor of two and thus a large number of sub-resistors and a precise orientation and identical resistance value are required.
As previously, the harmonic filtering is applied within each bridge branch. Because each individual bridge branch filters the same number of harmonics, the bridge voltage of these harmonics is also filtered. The number of necessary pinning directions in one bridge doubles with each filter. Thus, there are 2 pinning directions in the original configuration without filter (see FIG. 1). With a filter for one harmonic, there are then 4 pinning directions (see FIG. 2). Each bridge branch requires at least four sensor elements, i.e. sub-resistors. If two harmonics are filtered, a total of 8 pinning directions is obtained. Each bridge branch then contains at least eight sensor elements. In this case, the complete bridge requires at least 16 sensor elements. A sensor consisting of two bridges in this respect requires at least 32 sensor elements.
A further requirement of a high accuracy magnetoresistive angle sensor results from the fact that the overall resistance of the measuring bridge should on the one hand adopt a given value, in order to be optimally evaluated and to be able to influence a measurement current in a desired region, and from the fact that the resistance value of each individual bridge resistor arrangement in the magnetic field-free state and the sub-resistors constituting this should adopt nominally identical resistance values. With regard to manufacture, this can only be achieved in most cases with great difficulty or not at all, such that moreover the desired trigonometric curves of the measurement signals and optimal evaluation cannot be achieved. It is therefore desirable to be able to influence each resistor arrangement and the overall resistance of the measuring bridge during the manufacturing process or subsequently, in order in particular to counter tolerances in manufacture. Diagonal bridge resistors are of identical configuration and a plurality of different pinning directions is required in order effectively to reduce harmonics.
A disadvantage of the prior art is that filtering of harmonics by means of magnetoresistive resistor arrangements can only be achieved with high manufacturing complexity. Furthermore, homogeneity of the resistance behaviour in particular of TMR- or GMR-based resistor arrangements can be achieved only with difficulty, since the resistance values may be widely scattered during production.
The object of the present invention is to propose a resistor arrangement for a magnetoresistive angle sensor which achieves improved harmonic filtering and highly precise angular resolution with reduced manufacturing effort and circuit complexity.
This object is achieved by an angle sensor according to the independent claims. Advantageous embodiments of the invention constitute the subject matter of the subclaims.